(1) Field of the Invention
The present invention relates to a subscriber terminal apparatus for connecting a plurality of subscriber lines with a remote switching station via a communication line.
(2) Description of the Prior Art
A subscriber terminal apparatus is provided to accommodate a plurality of subscriber units (for example, telephone units) at locations remote from a switching station and to connect a plurality of subscriber lines from the subscriber units to the switching station via communication lines. Some of the subscriber lines in the subscriber terminal apparatus are not connected to any subscriber units and are provided for new subscribers which will be added to the subscriber terminal apparatus in the future. These subscriber lines are hereinafter called the vacant subscriber lines.
The subscriber terminal apparatus includes a concentrator connected to the communication line, and a distribution frame (DF) connected to the subscriber lines. All the subscriber lines in the service range are connected to subscriber terminals of the distribution frame. Within the distribution frame, the vacant subscriber lines are not connected to the concentrator, and only the accommodated subscriber lines are connected to the concentrator. When a new subscriber is added to the subscriber terminal apparatus, the subscriber line of the new subscriber unit and a line from the concentrator are connected within the distribution frame (DF). By connecting the corresponding subscriber terminal of the DF to the concentrator, it is possible for the subscriber line from the new subscriber unit to be connected to the switching station through the subscriber terminal apparatus. It is desirable to provide an apparatus which ensures an easy and efficient maintenance of subscriber units accommodated in the apparatus.
FIG. 6 shows a known subscriber terminal apparatus for connecting a plurality of telephone lines to a switching station which is remote from the telephone units. In FIG. 6, a switching station 51 and a plurality of telephone units 53 are connected by a subscriber terminal apparatus 55. The subscriber terminal apparatus 55 has a concentrator 57 (or a multiplexer) and a distribution frame 56 (or a cross-box).
The switching station 51 and the concentrator 57 are interconnected by a communication line 52. Lines of the concentrator 57 linked to the communication line 52 are connected to concentrator terminals of the distribution frame (DF) 56. On the other hand, the respective subscriber lines 54 from the telephone units 53 are connected to subscriber terminals of the distribution frame (DF) 56. Some of the subscriber lines 54 are not connected to telephone units and are provided for new subscribers which will be added to the subscriber terminal apparatus 55.
The number of the subscriber terminals of the distribution frame (DF) 56 to which the subscriber lines 54 are connected is greater than the number of the concentrator terminals of the distribution frame (DF) 56 to which the concentrator 57 is connected. In FIG. 6, F1 indicates the number of the concentrator terminals of the distribution frame (DF) 56, and F2 indicates the number of the subscriber terminals of the distribution frame (DF) 56. Usually, the number F2 of the distribution frame is two or three times as great as the number F1.
When a new telephone unit is added to the subscriber terminal apparatus, the corresponding subscriber terminal of the DF 56 and a concentrator terminal of the DF 56 are manually connected using a jumper line or the like, as indicated by a dotted line in FIG. 6. By performing the above mentioned connection relating to the DF 56, the newly added telephone unit is accommodated in the subscriber terminal apparatus, and the telephone unit can communicate with another telephone unit through the switching station.
If the number of telephone units 53 accommodated in the subscriber terminal apparatus has increased and exceeds the number of concentrator terminals of the DF 56, it is impossible to connect the subscriber lines of the additional telephone units to the concentrator 57 via the DF 56. In such a case, it is necessary to install an additional subscriber terminal apparatus, although the distribution frame 56 still has the vacant subscriber lines 54.
In the conventional apparatus described above, it is necessary that the subscriber terminal of the DF 56 and the concentrator terminal of the DF 56 be manually connected using a jumper line when the addition of a new subscriber unit is needed. It is necessary that the existing connection mentioned above be modified when the change of a certain subscriber unit is needed. In order to carry out the maintenance of subscriber units in the conventional apparatus, a manual connection change operation, relating to the distribution frame of the apparatus, must be performed by a maintenance person. In many cases, the subscriber terminal apparatus 55 is arranged at a location remote from the switching station, and no maintenance person is available at the remote location. Thus, it is necessary that a maintenance person who is stationed at the switching station goes to the location of the apparatus to perform the connection change operation of the distribution frame. In addition, the connection change operation mentioned above must be carefully performed by the maintenance person without making a mistake.
It is desirable that the maintenance of subscriber units in the subscriber terminal apparatus be directly or automatically carried out under the control of the switching station. However, in the case of the conventional apparatus described above, it is difficult to efficiently carry out the maintenance of subscriber units under the control of the switching station. The method of management of the maintenance of subscriber units by the switching station is that connection data indicating the connections of the subscriber lines 54 of the subscriber terminal apparatus 55 is printed out and the maintenance operation of the distribution frame 56 is performed by a maintenance person in accordance with the printed-out connection data. The cost of the maintenance operation of the distribution frame is therefore high.